This invention relates in general to prosthetic devices and in particular to a device and method for securing a prosthetic insert to a support member, such as a natural bone.
Prosthetic devices for the replacement of damaged or deteriorating portions of anatomy are well known in the art and are not necessarily restricted by the particular nature of the anatomy which needs replacing. Prosthetic devices range from full limb replacement types to those for small joint and bone replacements and regardless of their particular shape and size, one criteria of all prosthetic devices is that there is a need to secure the prosthetic device in place so that it functions properly.
Certain prosthetic devices which insert into the intramedullary canal of a bone may incorporate surface contouring to aid in this securing, and although cement may also be used, a primary contributor to the overall rigidity of the prosthesis is the surface contouring. Typical of this type of device are femoral head prostheses which insert into the shaft of the femur. However, there are certain areas of the anatomy which may need replacement of reconstruction and which do not have either the shape or bone mass for receiving an inserted prosthetic portion. Consider the innominate bone and in particular, the acetabulum. When both parts of the ball and socket full hip joint connection need replacement or reconstruction, the femoral head must be replaced with a prosthetic ball-shaped member and the acetabulum must be lined with a socket or cup member in order to receive this ball-shaped member. One method of affixing this acetabular cup into the acetabulum is by a layer of acrylic cement packed between the acetabulum and the acetabular cup.
While a variety of prosthetic devices for hip joint replacement and repair are known in the art, none of these prior art devices nor their corresponding method of use achieve the desirable results which the present invention achieves. The following listed patents provide an indication of some of these prior art prosthetic devices and methods.
______________________________________ Pat. No. Patentee Issue Date ______________________________________ 4,092,741 David 6/06/78 3,740,769 Haboush 6/26/73 3,641,590 Michele 2/15/72 3,521,302 Muller 7/21/70 3,683,421 Martinie 8/15/72 3,656,184 Chambers 4/18/72 ______________________________________
David discloses a prosthetic device for use as a hip joint which includes a substantially spherical portion locatable in the acetabular fossa of a pelvis bone, and a longitudinal portion locatable in a thigh bone. The spherical portion is anchored within the fossa by a holding member which is fixed to the fossa. The FIG. 2 embodiment discloses a cup which is anchored to the pelvis bone by three threaded fasteners.
Haboush discloses a prosthesis for hip joints which is formed as a one-piece unit and includes a spike-like stem that is inserted axially into the femur. An arm integral with the upper end of the stem projects outwardly at an obtuse angle relative to it and a ball is attached at the outer end of the arm connecting the prosthesis to the acetabulum or artificial socket, whichever is used. The ball and socket interface includes a series of Teflon plugs to aid in lubricating the sliding movement between these two surfaces.
Michele discloses a selective, individualized technique for acetabulum socket replacement including use in conjunction with a hip replacement prosthesis for a total hip replacement. The prosthetic portion is anchored into the bone by a main pin and one or more auxiliary pins.
Muller discloses an artificial joint which is formed by a pair of substantially complementary-shaped prosthetic members which have a resiliently compressible slide member disposed between them. The resiliently compressible slide member maintains the prosthetic members in spaced relation when in an unladen state but allows the prosthetic members to contact each other when in a laden state.
Martinie discloses a prosthetic joint assembly for supporting first and second bone members for relative movement between such members. The joint assembly includes a pin member adapted to seat in a pocket formed in the first bone member and a socket assembly adapted to be mounted in the second bone member. Furthermore, there is a connecting member connected at one end to the pin member and having at its opposite end a ball journalled in the socket assembly. The socket assembly attaches to the bone by a layer of acrylic material which appears to be preformed prior to locating it in the reamed and contoured bone.
Chambers discloses an artificial hip joint comprising a socket member and an inter-fitting ball member, in which dislocation of the joint is positively prevented by retaining means forming part of the socket member. The retaining means are constituted by extensions of the socket member beyond its diametral plane which define an opening into the socket smaller than that of the socket at the diametral plane. The socket includes ribs which are engaged by the plastic cement that secures the socket to the bone.
A further prior art disclosure is provided by pages D15 and D16 of a Zimmer Catalog. These pages discuss the procedure of bone preparation and prosthetic implant for a total hip replacement. Once the acetabulum is prepared by reaming, four holes are drilled into the bone and filled with acrylic cement prior to the coating of the acetabulum area with securing cement.
The prior art devices which do use an acrylic cement to secure the prosthetic cup to the acetabulum do not disclose a simple an effective means to control cement thickness. Although the ideal thickness of the cement is not necessarily agreed upon by all orthopedists, most orthopedists do generally concur with the concept that the amount of cement between the prosthetic insert (acetabular cup) and the support member (acetabulum) should be predictable and of a uniform thickness throughout the interface region. Another feature of the prosthesis implanting procedure which many orthopedists agree upon is that the acetabular cup should not rest directly on the bone surface of the acetabulum.
The invention disclosed herein provides a cement spacer concept and method for use with prosthetic inserts for controlling the uniformity and thickness of the cement which is applied between the prosthetic insert and its supporting bone member.